Download OTBA material for class VIII - Kendriya Vidyalaya Anantapuram

KENDRIYA VIDYALAYA SANGATHAN: HYDERABAD REGION
OPEN TEXT-BASED ASSESSMENT MATERIAL FOR CLASS VIII (Science)
Theme2: GLOBAL WARMING
Global warming is the increase in the average measured temperature of the Earth’s near
surface air and oceans. The increase in globally averaged temperature since the mid-twentieth
century is very likely due to observed increase in greenhouse gas concentrations via an
enhanced greenhouse effect. Natural phenomena such as solar variation combined with
volcanoes probably had a small warming effect.
Environmental Effects: The effects of global warming on the environment and human life
are numerous, varied, accelerating and taking scientists studying global warming by suspense.
Rising sea level, glacier retreat, Arctic shrinkage and altered pattern of agriculture are cited as
direct consequences of human activities.
Social Effects: Agriculturally Dr. Sylvan H. Whittwer believes that global warming is good for
the human race because it helps increase food production, History reveals that for food
production, warming is better than cooling. Dr. Whittwer says that carbon di-oxide is an
essential nutrient for the production of food and food is one of the most important things in
our lives. As the temperature rises more farmland will be open towards the poles and the
length of the growing season will also lengthen.
Increasing amounts of greenhouse gases in the atmosphere and global warming
could also lead to more health concerns. As temperature increase towards the poles, similar to
farmland, insects and other pests migrate towards Earth’s poles. Some insects carry diseases
such as malaria and dengue fever. This could lead to 50 to 80 million cases of malaria. With an
increase on heat waves there will be more people who will suffer from heatstroke, heart
attacks and other ailments aggravated by the heat. Hot conditions could also cause smoke
particles and noxious gases to linger in the air and accelerate chemical reactions that generate
other pollutants.
Global warming causes the oceans to
warm and expand inducing a rise in sea level.
Eventually, the rising water could take away
land inhabited by people forcing them to
move. Warming of oceans could also
promote toxic algae which can lead to
cholera.
Over the past century, the earth has increased in temperature by almost 0.5 degree Celsius
and many scientist believe, this is because of an increase in the concentration of the main
greenhouse gases- carbon di-oxide, methane, nitrous oxide and fluorocarbons. People are now
calling this climate change over the past century, the beginning of global warming. Fears are
that people keep producing such gases at increasing rates, the result will be negative such as
more severe floods and droughts, increasing prevalence of insects, sea level rising and earth’s
precipitation may be redisturbed.
Carbon di-oxide is emitted into the air as humans
exhale, burn fossil fuels for energy and deforests the
planet. As the abundance of the trees declines, less
carbon di-oxide can be recycled. As we burn them
down, carbon is released into the air and the carbon
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bonds with oxygen to form carbon di-oxide, adding to the greenhouse effect.
Methane is formed when plants decay and where there is very little air. It is often called
swamp gas. It stays in the atmosphere for only 10 years but traps 20 times more heat than
carbon di-oxide. Nitrous oxide is another green house gas. It is primarily used as an anesthetic
because it deadens pain and for this characteristic is called laughing gas. It is released naturally
from oceans and by bacteria in soils. Each year we add 7 to 13 million tons into the atmosphere
by using nitrogen based fertilizers, disposing of human and animal waste in sewage treatment
plants, automobile exhaust and other sources. It is important to reduce emissions because the
nitrous oxide we release today will still be trapped in the atmosphere 100 years from now.
The greenhouse effect is changing
the climate of the earth. Rapidly rising levels of
greenhouse gases due to the burning of coal, gas
and oil are one of the contributing causes of global
warming.
Unless we reduce greenhouse emissions
we cannot expect the effects of global warming to
have catastrophic consequences for wildlife around the world. From plankton to penguins to
polar bears the greenhouse effect is harming our animals forever changing their natural
habitats. A recent study says that the scientist is now predicting that a quarter of the world’s
animals and plant life would face extinction by 2050 due to climate change.
In the Arctic, global warming is already responsible for the loss of sea ice, which
scientist believes to be affecting the health of polar bears and reducing their population. The
polar bears hunting season is being cut short due to warmer temperatures, melting their seaice hunting ground at a faster rate. As a result polar bears now have less food to eat and to
raise their young. It is doubtful that polar bears could ever survive if there is a complete loss of
the Arctic’s summer sea-ice cover according to the International Arctic Science committee.
Wales, Caribou, Trout, Coral reefs, Monarch butterflies, the Arctic fox and songbirds are
just some of the species in danger from the effects of greenhouse gases. And if our wildlife is
threatened by global warming then it goes to
reason that so are we.
Climate change is changing our
economy, health and communities in diverse
ways. Climate change will have a significant
impact on the sustainability of water supplies in
the coming decades. A new analysis, performed
by consulting firm Tetra Tech for the Natural Resources Defense Council (NRDC), examined the
effects of global warming on water supply and demand in the United States. The study found
that more than 1,100 countries will face higher risks of water shortages by mid-century as the
result of global warming.
Thankfully, there are simple things that we can do right now to reduce the effects of global
warming and help save our wildlife.
Sample Questions:
1. Name two greenhouse gases. (1 mark)
2. How the melting of sea-ice would affect
the polar bears? (2 marks)
3. How does global effect have positive effect
on social life? (2 marks)
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